The present invention relates to an information recording/reproduction apparatus, such as a DVD, CD-ROM, CD, CD-R, or LD apparatus, which has a mechanism which tightly fastens the disc between a turntable and a clamper when an information recording disc, such as DVD, CD-ROM, CD, CD-R or LD, is rotated, and a rotation monitoring mechanism for the information recording disk assembled into the information recording/reproduction apparatus.
The DVD apparatus, for example, has been provided with a rotation monitoring mechanism for monitoring a rotation state of a DVD as an information recording disc.
A main role of the rotation monitoring mechanism is to generate a signal which is utilized for checking as to if the DVD has reliably been stopped in rotation after a STOP/EJECT button is pushed with intention of taking the DVD out of the apparatus.
Another role of the rotation monitoring mechanism is to generate a signal which is utilized for checking as to if the rotational speed of the DVD, for example, is abnormally high.
Yet another role of the rotation monitoring mechanism is to generate a signal utilized for the rotation servo system.
FIG. 2 shows a first related rotation monitoring mechanism designed for performing those roles, which indirectly detects a rotation state of a disc (DVD) 990 by detecting a rotation state of a turntable 910 for supporting and rotating the disc 990. The related rotation monitoring mechanism includes the turntable 910, a magnetic sensor 940 mounted on a small board 930, which is located in a small gap between the turntable and the upper face of a DC motor 920 for driving the turntable 910, and magnets (not shown) which are circularly buried in the lower face of the turntable 910 at a predetermined pitch so as to pass through right above the magnetic sensor 940 when the turntable 910 is rotated.
In FIG. 2, reference numeral 970 is a damper of which the cross section is shaped like H laid laterally. The disc 990 is tightly fastened between the damper 970 and the turntable 910. Usually, the front loading type DVD apparatus includes such damper 970.
A recess 972 into which a top portion of protrusion 910a formed on the central portion of the turntable 910 is to be inserted is formed in the lower side of the camper 970. Usually, a magnet 971 (or any other metal plate, e.g., an iron plate, magnetically attracted) is buried in the bottom of the recess 972. An iron plate 910a1 (or magnet) is attached to the top face of a protrusion 910a of the turntable 910. The magnet 971 and the iron plate 910a1 bring the camper 970 into press-contact with the turntable 910 magnetically (or by the utilization of a magnetic attraction force) in order to firmly hold the disc 990 being fastened between the damper 970 and the turntable 910.
Reference numeral 980 designates a chucking plate for rotatably holding the damper 970. A main board, not shown, (usually provided separately from the small board 930) of the DVD apparatus is provided under the DC motor 920.
The user sets a disc 990 on a tray (not shown) of the front loading mechanism of the DVD apparatus. Then, the container with the disc located thereon transports the disc 990 to a predetermined position in the innermost part of the apparatus. Thereafter, the DC motor 920, the turntable 910, and the board 930, which have been at locations not in contact with the tray in the lower part of the apparatus, are lifted by a lifting mechanism through an opening formed in the tray up to a predetermined position such that a supporting face of the turntable 910 for the disc 990 is situated above the tray.
At this predetermined position, the turntable 910 supports the disc 990 instead of the tray. The bottom face of the damper 970 is pressed against the top face of the central part of the disc 990. That is, the disc 990 is tightly fastened between the turntable 910 and the damper 970.
Namely, the magnetic sensor 940 in the first related rotation monitoring mechanism detects a rotation state of the turntable 910 in the form of variation of a magnetic field developed from the magnet of the rotation monitoring mechanism, which is provided in the bottom face of the turntable 910.
In the first related rotation monitoring mechanism thus constructed, where a length of a rotary shaft 921 of the DC motor 920 is long, the motor rotation is unsteady. To avoid this, the length of the rotary shaft is selected to usually be short, about 5 mm. It is necessary that the diameter of the turntable 910 is selected so that it does not cover an information recording area of the disk 990. Further, the DC motor 920 is required to generate a torque large enough to turn the disc 990. Accordingly, the diameter of the DC motor 920 is selected to be substantially equal to that of the turntable 910. For this reason, the magnetic sensor 940 mounted on the small board 930 is located in a small gap of about 5 mm wide between the turntable 910 and the upper face of the DC motor 920 for driving the turntable 910, in order to detect a variation of a magnetic field developed from the magnet provided on the bottom face of the turntable 910. This necessitates the use of an expensive Hall element for the rotation detector that may be mounted on the small board 930 (viz., the magnetic sensor 940 consists of a Hall element.).
Thus, the rotation monitoring mechanism rejects the use of a relatively inexpensive photo sensor, but requires the use of an expensive Hall element (in some cases, additional circuits, for example, an amplifier for amplifying a weak signal output from the Hall element). Further, the small board 930 on which the Hall element is mounted is separated from the main board since a positional limitation is present for the sensor mounting and it must be designed to be movable. This fact presents a hindrance to the effort of reducing the cost to manufacture.
A second related rotation monitoring mechanism is disclosed in Japanese Patent Publication No. 7-56726A. In the mechanism, a synchronizing mark is attached to the disc in advance. It is used for detecting a rotation state of the disc per se. In the rotation monitoring mechanism, a photo sensor for detecting the synchronizing mark is provided at a position under the disc, outside the DC motor for driving the disc, and relatively close to a position where the synchronizing mark passes through.
The second related rotation monitoring mechanism allows the use of a relatively inexpensive photo sensor, but it is disadvantageous in that the synchronizing mark is indispensably attached to the disc. This leads to increase of manufacturing cost. Further, the rotation monitoring mechanism is incapable of monitoring a disc not having the synchronizing mark. Further, the board on which the photo sensor is mounted is required in addition to the main board since a positional limitation is present for the sensor mounting. This fact presents a hindrance in realizing cost reduction.
A third related rotation monitoring mechanism shown in FIGS. 3 and 4 is disclosed in Japanese Utility Model No. 3060766. In the figure, members similar to the first related art are designated by the same reference numerals used for explaining the first related art, and detailed explanation is omitted.
In the mechanism, windows 1173A and shield portions 1173B are alternately and circularly formed on a damper 1170 at a predetermined pitch as a detected member 1173. A photo emitter 1140A and a photo detector 1140B are respectively fitted into a holder 1140C to constitute a-sensor unit 1140. A reflector 1180 is arranged at an intersection of optical axes of the photo emitter 1140A and the photo detector 1140B so that light emitted from the photo emitter 1140A and passed through one of the windows 1173A is reflected to be detected by the photo detector 1140B. A shield wall 1140C1 is provided between the photo emitter 1140A and the photo detector 1140B to prevent erroneous detection.
When the camper is rotated together with the turntable 910, the windows 1173A and the shield portions 1173B are alternately pass through a space between the photo emitter 140A and the photo detector 140B, whereby light transmission/interception is detected.
The third related rotation monitoring mechanism detects a rotation state of the information recording disc with the aid of the clamper. Therefore, there is no need of using a synchronizing mark attached in advance to the information recording disc. Accordingly, the rotation monitoring mechanism is capable of monitoring a rotation state of any type of the information recording disc.
However, due to the necessity of providing the reflector 1180 and the shield wall 1140C1, the structure of mechanism becomes complicated and large space for the sensor unit 1140 is required. Thereby the manufacturing cost reduction cannot be attained.
Further, according to the configuration, the optical length between the photo emitter 1140A and the photo detector 1140B becomes long. Thereby the possibility of erroneous detection rises.
Still further, when the damper 1170 is rotated eccentrically due to unsteady rotation of the turntable 910 or the like, the windows are horizontally deviated from the predetermined position and thereby the light interception/transmission may be erroneously detected.
Accordingly, an object of the present invention is to provide a rotation monitoring mechanism and an information recording/reproduction apparatus, which are capable of accurate monitoring a rotation of a disc irrespective of a type of the disc, and capable of reducing the manufacturing cost.
In order to achieve the above object, according to the present invention, there is provided a mechanism for monitoring rotation of an information recording disk, comprising:
a turntable on which the information recording disk is disposed;
a damper coaxially rotated with the turntable while fastening the information recording disk onto the turntable;
a sensor unit including a photo emitter and a photo detector opposed to each other such that respective optical axes are aligned on the straight line; and
an interception member formed with the damper for periodically intercepting light emitted from the photo emitter so that the sensor unit detects the damper rotates together with the information recording disk.
Preferably, the interception member includes a plurality of shield plates for intercepting the light emitted from the photo emitter, which are circularly arranged on the camper at a predetermined pitch such that the center of the circular arrangement is coincident with the rotation center of the clamper. Here, the respective shield plates extend in a direction perpendicular to a rotation plane of the clamper.
Preferably, the interception member includes:
a transparent cylindrical member formed on the damper so as to extend in a direction perpendicular to a rotation plane of the damper such that the central axis thereof is coincident with the rotation center of the clamper; and
a plurality of shield patterns for intercepting the light emitted from the photo emitter, which are arranged on the outer circumferencial wall of the cylindrical member at a predetermined pitch.
Preferably, the interception member includes a cylindrical member formed on the damper so as to extend in a direction perpendicular to a rotation plane of the damper such that the central axis thereof is coincident with the rotation center of the clamper. Here, the circumferencial wall of the cylindrical member includes first portions made of a light-transparent material and second portions made of a light-opaque material which are arranged alternately at a predetermined pitch.
The interception member periodically crosses the optical path between the photo emitter and the photo detector, whereby light transmission/interception is detected without providing a reflector and a shield wall between the photo emitter and the photo detector as in the third related mechanism.
Therefore, the overall structure of the mechanism becomes simple and a large space for the sensor unit is not required. Accordingly, the manufacturing cost can be remarkably reduced.
Furthermore, since the optical length between the photo emitter and the photo detector can be shorten and simplified, the erroneous detection of the light transmission/interception can be remarkably reduced.
Still further, even if the clamper is eccentrically rotated due to unstable rotation of the turntable or the like, since the deviated direction of the detected member is in parallel with the optical path of the light emitted from the photo emitter, the influence of the eccentric rotation leading the erroneous detection of the light transmission/interception can be remarkably reduced.
It is noted that the photo emitter and the photo detector of the sensor unit are extremely low in cost. This leads to reduction of the cost to manufacture the rotation monitoring mechanism. In addition, according to the above configuration, an S/N ratio of the sensor unit may be increased. Therefore, if the output power of the photo emitter somewhat reduces by its aging, no problem arises in the sensor unit. The lifetime of the rotation monitoring mechanism is elongated.
Preferably, the sensor unit is mounted on a circuit board commonly used for the turntable and the clamper.
Therefore, there is no need of using a dedicated board having the sensor unit provided thereon. As a result, cost reduction of the rotation monitoring mechanism of the present invention is realized.
According to the present invention, there is also provided a mechanism for monitoring rotation of an information recording disk, comprising:
a turntable on which the information recording disk is disposed;
a damper coaxially rotated with the turntable while fastening the information recording disk onto the turntable;
first reflection members having a first reflectivity and second reflection members having a second reflectivity different from the first reflectivity, which are circularly and alternately arranged on the damper at a predetermined pitch; and
a reflection-type sensor unit for detecting reflectivity of emitted light therefrom which is varied by the first and the second reflection members to detect that the damper rotates together with the information recording disk.
Preferably, the sensor unit is mounted on a circuit board commonly used for the turntable and the clamper.
According to the present invention, there is provided an information recording/reproduction apparatus for an information recording disk, comprising the rotation monitoring mechanism as described above.
Also according to the above configuration, the cost reduction can be realized.